Where can blender splash scenes be downloaded?
The splash for 2.76 comes from the Alike short. I'm not sure exactly what you're looking for, but you can download the splash image itself here. And browse the history of all splashes here. Note that the 2.76 splash was mistakenly labeled as a 2.75 splash, so there appears to be two 2.75 splashes and no 2.76 splash.

As far as I know, the source files for Alike aren't available. However, you can find the sources for more recent splash scenes on the blender cloud.